1. Field of the Invention
The present invention relates to an electrostatic actuator driven by electrostatic force and a camera module using the electrostatic actuator.
2. Discussion of the Background
Heretofore, as an electrostatic actuator, there has been proposed a constitution of a type shown in, for example, FIG. 26 (for example, refer to Japanese Patent Laid-Open No. 140367/1996). A conventional electrostatic actuator shown in FIG. 26 is constituted by a slider (or movable section) 101 and two stators 102 and 103 sandwiching the slider 101 from above and from below. The respective stators 102 and 103 are arranged with two series of electrodes 102a, 102b, 103a and 103b and a total of four series of electrodes are provided by upper and lower sets of the stators. Further, the slider 101 is provided with electrode portions 101a and 101b formed in a projected shape to be opposed to the electrodes of the stators.
Further, pitches and electrode widths of the respective electrodes 102a, 102b, 103a and 103b provided at the stators 102 and 103 and the electrode portions 101a and 101b provided at the slider 101 are respectively the same. Further, in the stators 102 and 103, the respective electrodes are arranged alternately such that two series of the electrodes respectively appear in turn in a predetermined direction. Further, the upper electrodes 102a and 102b of the stator 102 and the lower electrodes 103a and 103b of the stator 103, are arranged such that phases of aligning pitches thereof are shifted from each other exactly by xc2xd.
Here, when voltage is applied between the electrode 102a of the stator 102 and the slider 101, by electrostatic force (Coulomb force) operated between the electrode 102a and the electrode portion 101a provided at the slider 101, the slider 101 is attracted to the stator 102 (such that the electrode 102a and the electrode portion 101a overlap). Successively, when the applied voltage is switched to the electrode 103a of the stator 103, by electrostatic force (Coulomb force) operated between the electrode 103a and the electrode 101b provided at the slider 101, the slider 101 is attracted to the stator 103 (such that the electrode 103a and the electrode 101b overlap).
When the voltage applied to the electrodes on the stator side is successively switched such that the electrodes are activated in the order 102axe2x86x92103axe2x86x92102bxe2x86x92103b, the slider 101 is driven macroscopically in the predetermined direction (right side in the drawing) of alternately arranged electrodes of the stators while vibrating upwardly and downwardly microscopically. When the order of applying the voltage to the electrodes of the stators is reversed such that the electrodes are activated in the order 102axe2x86x92103bxe2x86x92102bxe2x86x92103a, the slider 101 is driven in a reverse direction (left side in the drawing) to the predetermined direction of alternately arranged electrodes of the stator.
However, according to such an arrangement, the following problem is posed. According to the conventional electrostatic actuator, driving force is changed depending on its altitude by influence of gravitational force and therefore, a distance of advancing the slider 101 in one step is changed. For example, when a direction of driving the slider 101 coincides with a vertical direction, in order to drive the slider 101 upwardly in the vertical direction, in applying voltage to the electrode of the stator, it is necessary to repeat the same step a plurality of times (for example, at a step of the electrode 102axe2x86x92103a by a plurality of times). Therefore, in order to realize firm driving operation in correspondence with all the altitude, the actuator is driven under the severest condition and therefore, there poses a problem that voltage is applied more than necessary, moving speed is reduced and power consumption for driving is increased.
Further, in order to realize driving operation in the above-described predetermined direction, it is necessary to accurately control the phases in arranging the electrodes 102a and 102b provided at the stator 102 and the electrodes 103a and 103b provided at the stator 103, further, it is necessary to accurately fabricate the electrode portions at two faces of the slider 101 opposed to the electrodes. Therefore, the cost is high owing to time and labor required for assembling, which poses a problem in realizing mass production.
It is an object of the invention to provide an electrostatic actuator resolving such a problem, realizing efficient driving operation, easy to fabricate and excellent in mass production performance and provide a camera module for executing focal point adjusting operation by using the electrostatic actuator.
In order to resolve the above-described problem, according to an aspect of the embodiment of the invention, in an electrostatic actuator having first electrode portion and second electrode portion arranged at predetermined intervals, the electrode portions including respectively a plurality of series of electrodes arranging successively in a predetermined direction, a slider arranged in the intervals, having electrode portions at side faces opposed to the first electrode portion and the second electrode portion and movable in the predetermined direction, an electrostatic capacitance detecting circuit configured to detect electrostatic capacitances between the plurality of series of electrodes of the first electrode portion or the second electrode portion and the electrode portions of the slider, and a driving circuit configured to drive the slider in the predetermined direction by applying voltages alternately between the plurality of series of electrodes of the first electrode portion or the second electrode portion and the electrode portions of the slider, the plurality of series of electrodes respectively selected based on a detected result of the electrostatic capacitance detecting circuit.
Further, according to another aspect of the embodiment of the invention, in an electrostatic actuator having first electrode portion and second electrode portion arranged at predetermined intervals, the first electrode portion including three series or more of electrodes arranging successively in the predetermined direction and said second electrode portion including a single series of electrodes extended in the predetermined direction, a slider arranged at the intervals, having electrode portions at a side face opposed to the first electrodes and movable in the predetermined direction, an electrostatic capacitance detecting circuit configured to detect electrostatic capacitances between three series or more of electrodes of the first electrode portion and the electrode portions of the slider, and a driving circuit configured to drive the slider in the predetermined direction by applying voltages alternately between the three series or more of electrodes of the first electrode portion or the second electrode portion and the electrode portions of the slider, the three series or more of series of electrodes respectively selected based on a detected result of the electrostatic capacitance detecting circuit.
Further, according to another aspect of the embodiment of the invention, in an electrostatic actuator having first electrode portion and second electrode portion arranged at predetermined intervals, the first electrode portion and second electrode portion including a plurality of series of electrodes arranging successively in a predetermined direction, a slider arranged in the intervals, having electrode portions at side faces opposed to the first electrode portion and the second electrode portion and movable in the predetermined direction, an electrostatic capacitance detecting circuit configured to defect an electrostatic capacitance between one electrode of either of the first electrode portion or the second electrode portion and all of the electrodes of other thereof, and a driving circuit configured to drive the slider in the predetermined direction by alternately applying voltages between the plurality of series of electrodes of the first electrode portion and the second electrode portion and the electrode portions of the slider, the plurality of series of electrodes respectively selected based on a detected result of the electrostatic capacitance detecting circuit.
Further, according to the embodiments of the invention, there is also provided a camera module having photographing elements, an electrostatic actuator having a lens at one end face orthogonal to the predetermined direction of the slider or at inside thereof and controller configured to control to drive the slider.